Hmm I don't know. The cherry blossoms scene was very clearly a finalisation of Sena's feelings and a way for her to move forward. They're family and they'll always be family. It's not meant to be romantic. And the Sena x Kiku romance build up was the entire manga. Heck, I'd call this a slow burn with how it's paced.
It was meant to be romantic as well. It seems many don't understand this story (cultural misunderstandings?), which is a shame. This kind of melancholic feeling is deeply rooted in Japanese literature and this specific meeting finalised where all of the main characters stand. There is subtext here I suggest you go back and try to understand.
Rereading this series again, I still disagree. The cherry blossom scene is melancholic but it's familial between the sisters, not romantic. In fact, I would even read it as a clear end to the romantic feelings, a closure, contributing to that melancholy, punctuated by them finally talking things out and even fully acknowledging the presence of the fiance.
